Heat absorbing temperature control devices and method

ABSTRACT

The increase of temperature in heat sensitive devices during heat generating conditions is prevented through the absorption of heat, by providing a hydrated salt such as Lithium Chloride, Magnesium Chloride, Magnesium Sulfate, Sodium Sulfate, Aluminum Oxide, Aluminum Sulfate, Aluminum Fluoride, Aluminum Nitrate, Lithium Nitrate, Sodium Borate, Beryllium Sulfate, Sodium Phosphate, Calcium Chloride, Zinc Sulfate, Aluminum Chloride, Zinc Chloride and the mixtures thereof, in an amount sufficient to effect the required heat absorption. Where the heat generating conditions are generated by a heat generator, separate and distinct from the heat sensitive device, the hydrated salt is supported in a position between the heat sensitive device and the heat generator. Where the heat sensitive device is itself the heat generator, the hydrated salt is contacted to the heat sensitive device either directly or indirectly.

RELATED APPLICATIONS

This is a Division of its parent application Ser. No. 08/709,516, nowabandoned which in turn claim the benefit of U.S. ProvisionalApplication Ser. No. 60/003,387 filed on Sep. 7, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to heat absorbing devices and a method forconstructing same. Said heat absorbing devices have heat absorbingchemicals, i.e. endotherms, which use their respective heats of reactionto cool and maintain and control the temperature and heat of heatsensitive devices. These endotherms comprise certain acids and theirsalts, certain bases and their salts, and certain organic compounds,which have never before been used in the manner described, disclosed andclaimed below.

Often, active cooling of electronic components, particularly delicate TRmodules, Impatt diodes, data recorders, containers for chemicals andmunitions, batteries and the like, is not feasible; and even when it isfeasible, it requires continuous high energy cooling, which taxes otherancillary engineering systems typical in missiles, aircrafts, railroads,trucks, automobiles, guns, nuclear reactor systems, related combatsystems, as well as commercial systems and technology.

The heat sinks of the prior art generally employ phase change materialcompositions (PCMs) for the absorption and dissipation of heat. Theconventional PCM materials are largely solid or fluidic in nature, i.e.liquids, quasi-liquids, or solids such as waxes or other meltablecompositions. However, these conventional PCMs have proven to sufferfrom many technical problems, as well as problems in their use andapplication. These problems include relatively low latent heats offusion, the inability to control the shape and form of such fluid PCMmaterials, as well as the unevenness of heating and cooling. Otherproblems include the need to provide a containment housing and thestress placed on the housing, resulting in frequent rupture and spillageof the PCM; the hazard to life and property due to PCMs' high heatcontent and flammability; and lastly, the uneven cooling hysteresis.

In addition, the known PCMs can spill hot fluids onto a human's skin,resulting in serious third degree burns due to the sticky contact natureof many hot wax and polymer or plastic phase change materials (PCMs) andthe high heat and sticky adherence to the skin. Ruptured non-CompositeFabric Endothermic Material (CFEM) or liquified bulk PC disks spilltheir content and cause flash fires, which spread as the PCM pours outduring heating in ovens and wax-filled disks are prone to fires, whichcan spread and flow out of stoves.

Applicant has addressed some of these and other PCM problems in his U.S.Pat. No. 4,446,916. Applicant has disclosed what he calls a compositefabric endothermic material (CFEM), providing devices especiallysuitable as heat sinks for aerospace and military use. The patented CFEMprovides an improved heat sink that absorbs heat at the meltingtemperatures of a compound embedded within a fibrous mesh or matrix. TheCFEM preferably comprises a phase change material, which is held bycapillary action and chemical adhesion to the fibers of the matrix. As aresult a greatly increased surface area for heat transfer is obtained;thus providing for controlled melting and thermal dissipation of thefusion cooling agent.

Applicant has also addressed some of the PCM problems in his pendingU.S. patent application Ser. No. 08/183,199, now U.S. Pat. No.5,709,914, the disclosure and contents of which are incorporated hereinas if more fully set forth. Such application addresses the need for animproved recyclable endothermic/exothermic/thermal storage method foruse in many commercial and civilian applications, particularly for food,home and commercial packaging operations. In this application, improvedCFEMs are disclosed, capable of being employed in a variety ofcommercial applications such as in the food industry where a need hasarisen for heat retaining or heat insulating containers, packages andthermal storage devices.

However, the active agents suggested in Applicant's pending U.S. patentapplication Ser. No. 08/183,199, now U.S. Pat. No. 5,709,914 are notuseful in the present inventive heat absorbing devices, as they areconcomitantly both endotherms and exotherms. (i.e. first, they absorbheat and then they give off heat to the item in connection with whichthey are being used, for the purpose of maintaining it warm.)

While they can accomplish some protection from high temperatures throughthe physical phenomenon of the absorption of their latent heat offusion, wherein the appropriate crystalline substance absorbs a quantityof heat to melt without a temperature rise to its surroundings, they aretotally unsuitable for applications relating to the absolute protectionof heat sensitive devices from high heat. After all, the heat they haveabsorbed, they must release. In other words, not only do they absorbheat but they also release heat, particularly when confined in a closedenvironment.

Another problem with the active agents or Applicant's, pending U.S.patent application Ser. No. 08/183,199, now U.S. Pat. No. 5,709,914 andthe prior art PCMs is that they are not capable of absorbing more than200 cal/gm. Thus, they can remove heat for only a short period of timerelative to mass and only at temperatures not exceeding 326° F.Consequently, they are not effective for applications requiring coolingat very high temperatures and for long periods of time as would beneeded, for example, in airplane and railroad crash recorders, missileelectronics, spacecraft devices, power supplies, data recorders employedas aircraft and railroad components and combat devices, and incommercial uses such as oven sensors, fire walls, nuclear reactors,munitions' boxes, chemical containers, batteries and automobile exhaustsystems.

Finally, these latent heat of fusion agents (PCMs) tend to burn atrelatively high temperatures raising the overall heat content of thesystem. In addition, the reversibility of the phenomena virtuallyguarantees that these agents will also transfer heat into the heatsensitive devices once said devices are at a lower temperature than therespective temperatures of the agents. Consequently, not only do theseagents operate as heat absorbing agents, but in closed environments theyalso operate as heat transfer agents to cause the very damage to theheat sensitive devices that these agents were intended to protect in thefirst place. This they do by re-releasing the absorbed heat to the heatsensitive device, thereby increasing the time or duration that the heatsensitive device is exposed to a high heat environment.

It is, therefore, the object of the present invention to overcome thedisadvantages set forth above and, in particular, to provide fornonreversible heat absorbing applications.

It is a further object of the present invention to provide improvedcoolant media for use in heat sensitive devices such as airplane andrailroad crash recorders, missile electronics, munitions boxes,clothing, firewalls, safe boxes, nuclear reactors, laser shields,thermal pulse shields, spacecraft devices, power supplies, datarecorders employed as aircraft and railroad components, combat devices,as well as in commercial uses such as oven sensors and the like.

It is another object of the present invention to provide heat absorbingagents for use in heat sensitive devices, said heat absorbing agentsbeing capable of absorbing heat at temperatures above 300° F.

It is another object of the present invention to provide heat absorbingdevices with mechanisms that utilize the chemical reactions of latentheat of formation, decomposition or dehydration in such mechanisms.

These objects as well as others will be found in detail in thedisclosure that follows below.

SUMMARY OF THE INVENTION

According to the present invention a heat absorbing device and methodare provided comprising endothermic agents capable of absorbing heat forthe cooling and maintenance of the temperature of heat sensitive devicesat acceptable levels. Such endothermic agents comprise certain acids andtheir salts, certain bases and their salts, certain hydrate salts andcertain organic compounds. This means that they absorb large quantitiesof heat to decompose or to dehydrate to either new and simpler,chemically stable chemical compounds, or to their individual componentelements.

This ability to absorb heat and irreversibly decompose makes them idealfor the thermal protection of heat sensitive devices in applicationswhere the integrity of the heat sensitive devices must be maintained,under exposure to specified conditions of extreme high heat.

The shape, size and physical characteristics of the heat absorbingdevices and likewise the steps of the method are dictated by the type ofthe heat sensitive device being protected, the heat sensitive device'sspacial limitations, the heat sensitive device's physical environmentand the heat generating conditions, to which the heat sensitive devicewill be subjected.

Similarly, the type and the amount of endotherms used in the heatabsorbing device and in the method are dictated by the heat sensitivityof the heat sensitive device; the maximum temperature at which the heatsensitive device can continue to be viable at; the extreme temperatures,to which the heat sensitive device will ultimately be subjected; thetime for which the heat sensitive device will be exposed to said extremeheat generating conditions; and the total thermal flux or thermal load,to which the heat sensitive device will be subjected.

Preferably, the endotherms can be boric acid; metal hydroxides and theirmixtures; carbonates and bicarbonates and their mixtures; salts ofacetic acid, salts of formic acid, salts of boric acid, and theirmixtures; paraldehyde, paraformaldehyde, and trioxane and theirmixtures; and hydrate salts and their mixtures. Further such endothermscan be supported within the device, via a(n) retaining matrix,packaging, encapsulation, microencapsulation, enclosure or structure toform a heat absorbing surface, device or structure.

The heat sensitive devices can be embedded within the endotherms; orthey can be surrounded by the endotherms; or the endotherms can line thewalls (inner or outer) of the closed container within which the heatsensitive device is placed; or in the alternative, the endotherms can beadhered to a substrate (flexible or non-flexible) capable of beingadapted to the size and shape necessary for use with said heat sensitivedevices.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative schematic graph of the four phases of the heatabsorption exhibited by Lithium Hydroxide and the phenomena observedduring such phases, when Lithium Hydroxide is used as an endotherm, inaccordance with the present invention;

FIG. 2 is an illustrative schematic graph of the four phases of the heatabsorption exhibited by Sodium Hydroxide and the phenomena observedduring such phases, when Sodium Hydroxide is used as an endotherm, inaccordance with the present invention;

FIG. 3 is an illustrative schematic graph of at least two phases of theheat absorption exhibited by Aluminum Hydroxide and the phenomenaobserved during such phases, when Aluminum Hydroxide is used as anendotherm, in accordance with the present invention;

FIG. 4 is an illustrative schematic graph of at least two phases of theheat absorption exhibited by Calcium Carbonate and the phenomenaobserved during such phases, when Calcium Carbonate is used as anendotherm, in accordance with the present invention;

FIG. 5 and FIG. 6 are graphs showing the natural delay in temperaturerise for Lithium Formate and Lithium Acetate thermal decompositionreactions;

FIG. 7 and FIG. 8 are graphs showing the natural rise in temperature ofconventional beryllium or wax heat sink when used with a flight datarecorder, as compared to the same flight date recorder's thermalperformance with a boric acid heat absorbing shield formed in accordancewith the present invention; and

FIG. 9 is a graph showing the use of a hydrated salt, i.e. MagnesiumSulfate Heptahydrate, in accordance with the present invention.

DETAILED DESCRIPTION

The features of the present invention will hereinafter be described indetail.

The present invention utilizes non-recyclable, non-reversible,endothermic chemical reactions, which make use of the latent heat ofdecomposition and dehydration reactions to provide new, improved andparticularly, efficacious endothermic cooling systems.

What makes these non-recyclable, non-reversible, endothermic chemicalreactions particularly appropriate for use in the inventive heatabsorbing device and method, is that these reactions have temperaturesof reaction that correspond to the temperature ranges taken intoconsideration by the design of heat sensitive devices such as flightdata recorders, electronics and related devices. Accordingly, thepresence of these reactions in the heat absorbing devices insures thatsaid heat absorbing devices act only as heat absorbers and not as heatgenerators; thereby being capable of maintaining the internaltemperature of the heat sensitive devices at a range between 100° C. and300° C., while said heat sensitive devices are being exposed to anexternal temperature range of 600° C. to 1100° C.

The compounds developed in the present invention provide endothermicchemical reactions, which are extremely stable in diverse environments,have long shelf life and high latent heats of reaction. Preferably, thecompounds contemplated by the present invention include: boric acid andsome borate salts; salts of acetic acid and formic acid; hydroxides oflithium, calcium, aluminum and sodium; carbonate salts of magnesium,lithium and silicon; paraldehyde, paraformaldehyde and trioxane; andhydrated salts.

Specifically, the present invention makes a broad claim to a device andmethod using endothermic agents which thermally decompose as follows:

1. Hydrated salts endothermically decompose to water and salt;

2. Paraldehyde, paraformaldehyde and trioxane endothermically decomposeto formaldehyde and thereafter to amorphous carbon, water, carbondioxide and ethane;

3. Low molecular weight acids endothermically decompose into water andoxides; and

4. Carbonate salts endothermically decompose into carbon dioxide and anoxide.

Generally, the inventive method involves taking an amount of endothermsufficient to effect the required heat absorption and either contactingsaid endotherm to the heat sensitive device, or supporting saidendotherm between the heat sensitive device and the heat generator so asto absorb the heat and prevent any increase in the temperature of theheat sensitive device. In either case, the amount of endotherm, the typeof endotherm, and the location of the endotherm can be determined on thebasis of the disclosure set forth below.

I. The following illustrates the endothermic reaction and heatabsorption of the aforementioned hydroxides when subjected to atemperature of reaction below 1100° C.

(a) LITHIUM HYDROXIDE: Lithium Hydroxide's use as an endotherm attemperatures below and up to 1100° C. is characterized by at least fourphases of heat absorption. FIG. 1 shows these four phases of heatabsorption, i.e. A, B, C and D, and the phenomena observed during suchphases. It is noted that the slopes of the graph are neither accuratenor precise but are only intended to be illustrative in nature.

Theoretically, the total amount of heat in calories absorbed by LiOHwhen exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B+C+D=Hrx

where

A=the amount of heat in calories absorbed by LiOH prior to melting;

B=the amount of heat in calories absorbed during actual melting phase ofLiOH;

C=the amount of heat in calories absorbed by LiOH once melting iscomplete and it begins approaching its temperature of decomposition; and

D=the actual amount of heat of decomposition of LiOH in calories.

(i) Calculating the Hrx for LiOH:

The amount of heat in calories absorbed during Phase A as LiOH'stemperature begins to rise from room temperature, i.e. 25° C. to itsMelting Point temperature of 462° C. is limited only by the specificheat of LiOH, i.e. the amount of calories absorbed by 1 mole of LiOH tochange 1 degree Celsius. Consequently, one can theoretically calculatethe Phase A heat absorption by using LiOH's specific heat of 11.87cal/deg mol or 11.87/23.9484 (g/mol)=0.4956 cal/deg g (see CRC, HANDBOOKOF CHEMISTRY & PHYSICS, 63rd EDITION, P. D-74 (1982-1983) as follows:(462° C.−25° C.)×0.4956 cal/deg g=217 cal/g. Thus, A=217 cal/g.

When the temperature of LiOH reaches its melting point, i.e. 462° C.,LiOH begins to melt. This begins Phase B. While the melting is going onand until LiOH is completely liquid there is no change in temperature(ergo the flat line at Phase B). The amount of heat in calories absorbedduring such phase B at 462° C. is 103.3 cal/g. see CRC, HANDBOOK OFCHEMISTRY & PHYSICS 63RD EDITION, P. B-252 (1982-1983)

Once LiOH has completely melted, its temperature begins to rise. Thisbegins phase C in FIG. 1. Just as in phase A, the amount of heatabsorbed during phase C is limited only by LiOH's specific heat of0.4956 cal/deg g. Thus, one can theoretically calculate the Phase C heatabsorption as follows: (1100° C.−462° C.)×0.4956 cal/deg g=316 cal/g,i.e. C=316 cal/g.

When the temperature of the melted LiOH reaches its temperature ofdecomposition, approximately 1100° C. LiOH begins to decompose, i.e.,

2LiOH decomposes to→Li₂O+2H₂O

This begins phase D. While the decomposition is going on and until LiOHis completely decomposed there is practically no change in temperature(ergo the flat line at Phase D). The amount of heat in calories absorbedduring such phase D at approximately 1100° C. is approximately 600cal/g.

Therefore, based on the discussion above, the theoretical amount of heatabsorbed by LiOH when used as an endotherm, is:

217 cal/g+103.3 cal/g+316 cal/g+600 cal/g=1236.3 cal/g.

It is seen from the foregoing that when LiOH decomposes at its specifiedtemperature of reaction to form Lithium Oxide, it absorbs a largequantity of latent heat of reaction. More importantly, however, a higheramount of latent heat is absorbed by the melting of LiOH and its heatcapacity up to 1000° C. The above suggests that LiOH should be very goodat absorbing 686 cal/g for the decomposition, an extra 316 cal/g for itsheat capacity up to 1100° C., 103.3 cal/g for its melting at 462° C. and217 cal/g for its heat capacity to 462° C.

In fact, when LiOH was actually used as an endotherm in the heatabsorbing device of the present invention it was determined that itactually absorbed 1207 cal/g.

(b) SODIUM HYDROXIDE: Sodium Hydroxide's use as an endotherm attemperatures below and up to 1100° C. is similarly characterized by atleast four phases of heat absorption. FIG. 2 shows these four phases ofheat absorption, i.e. A, B, C and D, and the phenomena observed duringsuch phases. It is noted that the slopes of the graph are neitheraccurate nor precise but are only intended to be illustrative in nature.

Theoretically, the total amount of heat in calories absorbed by NaOHwhen exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B+C+D=Hrx

where

A=the amount of heat in calories absorbed by NaOH prior to melting;

B=the amount of heat in calories absorbed during actual melting phase ofNaOH;

C=the amount of heat in calories absorbed by NaOH once melting iscomplete and it begins approaching its temperature or decomposition; and

D=the actual amount of heat of decomposition of NaOH in calories.

(i) Calculating Hrx for NaOH:

The amount of heat in calories absorbed during Phase A (FIG. 2) asNaOH's temperature begins to rise from room temperature i.e, 25° C. toits Melting Point temperature of 322° C. see CRC, HANDBOOK OF CHEMISTRY& PHYSICS, 63RD EDITION, P. B-253 (1982-1983) is limited only by thespecific heat of NaOH, when NaOH is a solid i.e. the amount of caloriesabsorbed by 1 mole of NaOH to change 1 degree Celsius. Consequently, onecan theoretically calculate the Phase A heat absorption by using NaOH'sspecific heat of 14.23 cal/deg mol or 14.23/39.9972 (g/mol)=0.3558cal/deg g see CRC, HANDBOOK OF CHEMISTRY & PHYSICS, 63rd EDITION, P.D-86 (1982-1983) as follows: (322° C.−25° C.)×0.3558 cal/deg g=105.6cal/g. Thus, A=105.6 cal/g.

When the temperature of NaOH reaches its melting point i.e. 322° C.,NaOH begins to melt. This begins Phase B (FIG. 2). While the melting isgoing on and until NaOH is completely liquid there is no change intemperature (ergo the flat line at Phase B). The amount of heat incalories absorbed during such phase B at 322° C. is 50.0 cal/g. see CRC,HANDBOOK OF CHEMISTRY & PHYSICS 63RD EDITION, P. B-253 (1982-1983).

Once NaOH has completely melted, its temperature begins to rise. Thisbegins phase C (FIG. 2). Just as in phase A, the amount of heat absorbedduring phase C is limited only by NaOH's specific heat of 0.3558 cal/degg. Thus, one can theoretically calculate the Phase C heat absorption asfollows: (1100° C.−322° C.)×0.3558 cal/deg g=276.8 cal/g i.e. C=276.8cal/g.

When the temperature of the melted NaOH reaches its temperature ofdecomposition, approximately 1100° C. NaOH begins to decompose, i.e.,

2NaOH decomposes to→Na₂O+2H₂O.

This begins phase D (FIG. 2). While the decomposition is going on anduntil NaOH is completely decomposed there is practically no change intemperature (ergo the flat line at Phase D). The amount of heat incalories absorbed during such phase D at approximately 1100° C. inapproximately 324 cal/g.

Therefore, based on the discussion above, the theoretical amount of heatabsorbed by NaOH when used as an endotherm, is:

105.6 cal/g+50 cal/g+276.8 cal/g+324 cal/g=756.4 cal/g.

It is seen from the foregoing that when NaOH decomposes at its specifiedtemperature of reaction to form Sodium Oxide, it absorbs a largequantity or latent heat of reaction. More importantly, however, a higheramount of latent heat is absorbed by the melting of NaOH and its heatcapacity up to 1000° C. The above suggest that NaOH should be very goodat absorbing 324 cal/g for the decomposition, an extra 276.8 cal/g forits heat capacity up to 1100° C., 50.0 cal/g for its melting at 322° C.and 105.6 cal/g for its heat capacity to 322° C.

In fact, when NaOH was actually used as an endotherm in the heatabsorbing device, it was determined that it actually absorbed 585 cal/g.

(C) ALUMINUM HYDROXIDE: Aluminum hydroxide's use as an endotherm attemperatures below and up to 1100° C., on the other hand, ischaracterized by at least two phases of heat absorption. FIG. 3 showsthese two phases of heat absorption,. i.e. A and B, and the phenomenaobserved during such phases. It is noted that the slopes of the graphare neither accurate nor precise but are only intended to beillustrative in nature.

Theoretically, the total amount of heat in calories absorbed by Al(OH)₃when exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B=Hrx

where

A=the amount of heat in calories absorbed by Al(OH)₃ prior todecomposing; and

B=the amount of heat in calories absorbed by Al₂O₃ once thedecomposition is complete.

(i) Calculating Hrx for Al(OH)₃

The amount of heat in calories absorbed during Phase A (FIG. 3) asAl(OH)₃'s temperature begins to rise from room temperature i.e. 25° C.to its temperature of Decomposition of approximately 200° C. has beenfound to be approximately 324 cal/g. Aluminum Hydroxide decomposes asfollows:

2Al(OH)₃ decompose to→Al₂O₃+3H₂O

While the decomposition is going on and until Al(OH)₃ is completelydecomposed there is practically no change in temperature (ergo the flatline at phase A). The amount of heat in calories absorbed during suchphase A is A=324 cal/g.

Once Al(OH)₃ is completely decomposed to Al₂O₃, Al₂O₃'s temperaturebegins to rise. This begins phase B in FIG. 8. The amount of heatabsorbed during phase B is limited only by Al₂O₃'s specific heat of0.1853 cal/deg g. see CRC, HANDBOOK OF CHEMISTRY & PHYSICS 63RD EDITION,P. D-53 (1982-1983).

Thus, one can theoretically calculate the Phase B heat absorption asfollows: (1100° C.−200° C.)×0.1853 cal/deg g=166.77 cal/g, i.e. B=166.77cal/g.

Therefore, based on the discussion above, the theoretical amount of heatabsorbed by Al(OH)₃ when used as an endotherm, is:

324 cal/g+166.77 cal/g=490.77 cal/g.

It is seen from the foregoing that when Al(OH)₃ decomposes at itsspecified temperature of reaction to form Aluminum Oxide, it absorbs alarge quantity of latent heat of reaction. More importantly, however, ahigher amount of specific heat is absorbed due to the heat capacity ofAl₂O₃ up to 1100° C. The above suggests that Al(OH)₃ should be very goodat absorbing 324 cal/g for the decomposition, and an extra 166.77 cal/gfor Al₂O₃'s heat capacity up to 1100° C.

In fact, when Al(OH)₃ was actually used as an endotherm in a heat sinkit was determined that it actually absorbed 510 cal/g.

II. The following illustrates the endothermic reaction and heatabsorption of the aforementioned carbonate salts, when they aresubjected to a temperature of reaction below 1100° C.

(a) CALCIUM CARBONATE: Calcium Carbonate's use as an endotherm attemperatures below and up to 1100° C., is characterized by at least twophases of heat absorption. FIG. 4 shows these two phases of heatabsorption, i.e. A and B, and the phenomena observed during such phases.It is noted that the slopes of the graph are neither accurate norprecise but are only intended to be illustrative in nature.

Theoretically, the total amount of heat in calories absorbed by CalciumCarbonate when exposed to temperatures below and up to 1100° C. can bemathematically represented by the following formula:

A+B=Hrx

where

A=the amount of heat in calories absorbed by CaCO₃ at its temperature ofdecomposition;

B=the amount of heat in calories absorbed by CaO as its temperaturerises.

(i) Calculating Hrx for CaCO₃

The amount of heat in calories absorbed during Phase A (FIG. 4) by CaCO₃at the temperature of Decomposition of approximately 825° C. has beenfound to be approximately 425.6 cal/g. see MERCK INDEX, TENTH EDITION,P. 228 (1983). Calcium Carbonate decomposes as follows:

CaCO₃ decomposes to→CaO+CO₂

While the decomposition is going on and until CaCO₃ in completelydecomposed there is practically no change in temperature (ergo the flatline at phase A). Thus, A=425.6 cal/g. It is noted that in the presenttheoretical calculations the amount of heat absorbed by CaCO₃ as itstemperature begins to rise from room temperature, i.e. 25° C. to itsactual temperature of decomposition has been omitted, for simplicity'spurposes.

Once CaCO₃ is completely decomposed to CaO, now CaO's temperature beginsto rise. This begins phase B in FIG. 4. The amount of heat absorbedduring phase B is limited only by CaO's specific heat of (19.57 cal/degmol)/(100.089 gr./mol)=0.1824 cal/deg g. see CRC, HANDBOOK OF CHEMISTRY& PHYSICS 63RD EDITION, P. D-59 (1982-1983).

Thus, one can theoretically calculate the Phase B heat absorption asfollows: (1100° C.−825° C.)×0.1824 cal/deg g=50.16 cal/g, i.e. B=50.16cal/g.

Therefore, based on the discussion above, the theoretical amount of heatabsorbed by CaCO₃ when used as an endotherm, is:

425.6 cal/g+50.16 cal/g=475.76 cal/g.

It is seen from the foregoing that when CaCO₃ decomposes at itsspecified temperature of reaction to form Calcium Oxide, it absorbs alarge quantity or latent heat of reaction. More importantly, however, ahigher amount of latent heat is absorbed by the heat capacity of CaO upto 1100° C. The above suggests that CaCO₃ should be very good atabsorbing 425.6 cal/g for the decomposition, and an extra 50.16 cal/gfor CaO's heat capacity up to 1100° C.

In fact, when CaCO₃ was actually used as an endotherm in a heatabsorbing device (heat shield) it was determined that it actuallyabsorbed 725.60 cal/g. This amount of heat is significantly higher thanthe amount of heat theoretically calculated above. This is logical whenone considers that (i) the theoretical calculations above did not takeinto consideration the heat absorbed by CaCO₃, during the time that itstemperature was rising from room temperature up to its temperature ofdecomposition (specific heat); and (ii) more likely than not, the CaCO₃was probably contaminated with small amounts of water, which has itsheat of vaporization; thereby adding to the total endothermic effectobserved during the testing of CaCO₃

(b) SILICON CARBONATE (SiCO₃): On the basis of the discussion set forthabove in connection with CaCO₃, it was theorized that Silicon Carbonateshould exhibit the same type of endothermic absorption effects. In fact,when Silicon Carbonate was used as an endothermic material it was foundthat:

(SiCO₃) decomposes to→SiO+CO₃ at 1100° C., and that it absorbs 380cal/gm for decomposition.

(c) MAGNESIUM CARBONATE (MgCO₃): Similarly, when Magnesium Carbonate wasused as endothermic material it was found that the starting endothermicmaterial is composed of Magnesium Carbonate (MgCO₃), Magnesium Hydroxide(Mg(OH)₂) and Water (H₂O). i.e., n MgCO₃:n Mg(OH):n H₂O; and that

n MgCO₃:n Mg(OH)₂:n H₂O decomposes to→nMgO+nCO₂ and nH₂O at 700° C. Theamount of heat absorbed during such decomposition was 285 cal/gm.

III. Other reactions which can provide endothermic cooling of heatsensitive devices, other surfaces and structures via heat absorption,i.e. endothermic mechanisms similar to those described above are asfollows:

(a) SODIUM BICARBONATE: The Thermal Decomposition of sodium bicarbonateabsorbs in excess of 350 cal/gm between 120° C. and 310° C. i.e.,

2NaHCO₃→Na₂CO₃+H₂O+CO₂

T=270° C.

ΔH_(r)=363 cal/g

(b) SODIUM BICARBONATE: The Thermal Decomposition of sodium bicarbonateabsorbs in excess of 320 cal/gm between 200° C. and 375° C. i.e.,

MW = 84.0 2 NaHCO₃ => Na₂CO₃ + H₂O + CO₂  ΔH° = 30.45 Kcal/mol Δ H_(f)°: −226.5  −102  −94.05 Δ H_(r) = (30,450 cal/mol)/ (84 g/mol) = 363cal/g

(c) BORIC ACID: In particular, it has been found that boric acid absorbslarge amounts of heat when decomposing, because boric acid decomposes instages over a range of temperatures to produce boron oxide and waterwhile absorbing nearly 400 cal/g. Borate salts act similarly foreffective heat absorption results.

Specifically, the Thermal Decomposition of Boric Acid absorbs in excessof 400 cal/gm between 120° C. and 350° C. i.e.,

MW = 62 169° C. 300° C. 2 H₃BO₃ => (2HBO₂ + 2H₂O) => B₂O₃ + 3H₂O ΔH_(f):−260 mp = 236° C. −302  −57.8 Kcal/mol Δ H = 53.6 Kcal/2 mol H₃BO₃ ΔH_(r) = (53,600 Kcal/2 mol) (2(62) g/2 mol ≧ 432 cal/g

IV. The following illustrate the endothermic reaction and heatabsorption of hydrated salts for the cooling of heat sensitive devices,other surfaces and structures via heat absorption mechanisms similar tothose described above when subjected to a temperature reaction below1100° C. Specifically the following hydrate salts provide effectiveendothermic cooling from 60° C. through 200° C.:

(a) HYDRATED SALT OF LITHIUM CHLORIDE: This reaction will provideendothermic cooling of electronic devices and other surfaces andstructures by the thermal decomposition of lithium chloride trihydrateabsorbing in excess of 440 cal/g between 90° C. and 150° C. i.e.,

LiCl · 3H₂O => LiCl + 3H₂O at 98° C. Δ H_(f)° : (−313.5) (−97)  (−173)Kcal ΔH_(r) = 42.4 Kcal/mol MW = 96.39 (42.4 Kcal/mole)/ 96.39 = 440cal/g

(b) HYDRATED SALT OF MAGNESIUM CHLORIDE:

MgCl₂ · 6H₂O => MgCl₂ + 6H₂O Δ H_(f)° : (−454) (−266)  (−346.8) ΔH_(r)is negative.

(c) HYDRATED SALT OF MAGNESIUM SULFATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of magnesium sulfateheptahydrate absorbing in excess of 350 cal/g between 120° C. and 250°C. i.e.,

MgSO₄ · 7H₂O => MgSO₄ + 7H₂O Δ H_(f)° : (−808.7) (−305.5)  (−404.6)ΔH_(r) = 98.6 Kcal/mol MW = 246.37 (98.6 Kcal/mole)/ 246.37 = 400.2cal/g

(d) HYDRATED SALT OF SODIUM SULFATE:

Na₂SO₄ · 10H₂O => Na₂SO₄ + 10H₂O Δ H_(f)° : (−1033.48) (−330.9)  (−578)ΔH_(r) = 124.58 Kcal/mol MW = 354.12 (124.58 Kcal/mole)/ 354.12 = 351.8cal/g

(e) HYDRATED SALT OF ALUMINUM OXIDE:

Al₂O₃ · 3H₂O => Al₂O₃ + 3H₂O Δ H_(f)° : (−613.7) (−384.84)  (−173.4)ΔH_(r) = 55.46 Kcal/mol MW = 155.96 (55.46 Kcal/mole)/ 155.96 = 355.6cal/g

(f) HYDRATED SALT OF ALUMINUM SULFATE:

Al₂(SO₄)₃ · 18H₂O => Al₂(SO₄)₃ + 18H₂O Δ H_(f)° : (−2118.5) (−820.98) (−1040.4) ΔH_(r) = 257.12 Kcal/mol MW = 666.14 (257.12 Kcal/mole)/666.14 = 385.98 cal/g

(g) HYDRATED SALT OF ALUMINUM FLUORIDE:

AlF₃ · 3H₂O => AlF₃ + 3H₂O Δ H_(f)° : (−349.1) (−311)  (−173.4) ΔH_(r) =64.7 Kcal/mol MW = 137.98 (64.7 Kcal/mole)/ 137.98 = 468.9 cal/g

(h) HYDRATED SALT OF ALUMINUM NITRATE:

Al₂(NO₃)₃ · 9H₂O => Al₂(NO₃)₃ + 9H₂O Δ H_(f)° : (−897.34) (−273.65) (−520.2) ΔH_(r) = 103.49 Kcal/mol MW = 375.01 (103.49 Kcal/mole)/375.01 = 275.98 cal/g

An additional endothermic effect may be obtained by the furtherdecomposition of Al₂(NO₃)₃.

(i) HYDRATED SALT OF LITHIUM NITRATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of lithium nitrate trihydrateabsorbing in excess of 320 cal/g between 50° C. and 120° C. i.e.,

LiNO₃ · 3H₂O => LiNO₃ + 3H₂O at 61° C. Δ H_(f)° : (−328.6) (−115.3) (−57.8) ΔH_(r) = 39.9 Kcal/mol MW = 123 (39.9 Kcal/mole)/ 123 = 324.4cal/g

(j) HYDRATED SALT OF SODIUM CARBONATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium carbonate decahydrateabsorbing in excess of 320 cal/g between 20° C. and 80° C. i.e.,

Na₂CO₃ · 10H₂O => Na₂CO₃ + 10H₂O: loses H₂O at 34° C. Δ H_(f)° :(−975.6) (−270)  (−57.8) ΔH_(r) = 127.6 Kcal/mol MW = 266 (127.6Kcal/mole)/266 = 480 cal/g

(k) HYDRATED SALT OF SODIUM BORATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium borate decahydrateabsorbing in excess of 350 cal/g between 200° C. and 375° C. i.e.,

Na₂B₄O₇ · 10H₂O => Na₂B₄O₇ + 10H₂O; at 320° C. Δ H_(f)° : (-1497)(−777.7) (−578) ΔH_(r) = 141.3 Kcal/mol MW = 382 (141.3 Kcal/mole)/382 =370 cal/g

(l) HYDRATED SALT OF BERYLLIUM SULFATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of beryllium sulfatequatrohydrate absorbing in excess or 300 cal/g between 90° C. and 450°C. i.e.,

BeSO₄ · 4H₂O => BeSO₄ · 2H₂O + 2H₂O; at 100° C. Δ H_(f)° : (−576.3)(433.2)  (−57.8) BeSO₄ · 2H₂O => BeSO₄ + 2H₂O; ΔH° = 31.6 (−433.2)(−286)  (−57.8) ΔH° = 31.6 ΔH_(r) = 65.53 Kcal/mol MW = 177.1 (65.53Kcal/mole)/177.1 = 370 cal/g

(m) HYDRATED SALT OF SODIUM PHOSPHATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of sodium phosphatedodecahydrate absorbing in excess of 300 cal/g between 80° C. and 150°C. i.e.,

Na₃PO₄ · 12H₂O => Na₃PO₄ + 12H₂O Δ H_(f)° : (−1309) (−460)  (−57.8)ΔH_(r) = 156.4 Kcal/mol MW = 377 (156.4 Kcal/mole)/377 = 412 cal/g

(n) HYDRATED SALT OF CALCIUM CHLORIDE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of calcium chloride hexahydrateabsorbing in excess of 300 cal/g between 220° C. and 350° C. i.e.,

CaCl₂ · 6H₂O => CaCl₂ + 6H₂O at 200° C. Δ H_(f)° : (−623.2) (−190) (−57.8) ΔH_(r) = 86.4 Kcal/mol MW = 219 (86.4 Kcal/mole)/219 = 395cal/g

(o) HYDRATED SALT OF ZINC SULFATE: This reaction will provideendothermic cooling of heat sensitive devices and other surfaces andstructures by the thermal decomposition of zinc sulfate heptahydrateabsorbing in excess of 300 cal/g between 220° C. and 350° C. i.e.,

ZnSO₄ · 7H₂O => ZnSO₄ + 7H₂O; at 280° C. Δ H_(f)° : (−735.1) (−233.8) (−57.8) ΔH_(r) = 96.7 Kcal/mol MW = 288 (96.7 Kcal/mole)/288 = 336cal/g

IV. Other endothermic reactions that have been found suitable for use inthe present inventive heat absorbing devices on the basis of theprinciples set forth above, are the decomposition of paraldehyde,paraformaldehyde and trioxane which, likewise, result in relativelylarge scale endothermics.

Several of the reaction products of the combination of theaforementioned materials such as lithium acetate, lithium formate andtheir hydrates may also be used. The graphs 5 and 6 show the naturaldelay in temperature rise for lithium formate and lithium acetatethermal decomposition reactions.

It has also been found that the salts of acetic acid and formic acid andtheir hydrates result in large scale endothermic reactions andabsorptions of large quantities of heat. Accordingly, these formic andacetic acid salts are also suitable for use in the present inventiveheat absorbing devices.

IV. The compounds of the present invention may be supported within theinventive heat absorbing device via composite fabric carriers ormatrices of the type discussed in Applicant's aforementioned applicationand in the prior noted patents, to form an endothermic structure.Additionally, the compounds can be supported up against the heatsensitive device as an endothermic structure via a retaining matrix,packaging, encapsulation, microencapsulation, enclosure, or structure;or by being suspended in other media; or they themselves may be used inbulk to form the endothermic structure. Irrespective of the support orwhether they themselves form the endothermic structure, said endothermicstructure can be measured, cut and fit to form (i) a heat absorbingsurface up against the heat sensitive device; (ii) an enclosure orcontainer, within which the heat sensitive device can be placed; or(iii) a thermal barrier structure or shield between a heat generator andthe heat sensitive device. If the compounds have not been formed into anendothermic structure, supported or otherwise, they could be simplydeposited around the heat sensitive device. Another embodiment, theretaining structure can be made of a low thermal conductivity material(or a thermal insulator) such as a plastic or polyamide.

Thus, in one embodiment of a heat absorbing device designed to protect aheat sensitive device from external heat, the endothermic compounds areenclosed within the walls of an enclosure. As used herein the termenclosure includes containers or box-like structures of any sizes orshape. In another embodiment of a similar heat absorbing device, thecompounds line the inner surface or the walls of the enclosure. In athird embodiment of said heat absorbing device, the endothermic compoundline the outer surface of the walls of the enclosure. In yet anotherembodiment of said device, the endothermic compounds are packed aroundthe heat sensitive device, surrounded with a retaining structure so thatit stays packed around the heat sensitive device, and the wrapped deviceis then placed in the enclosure. The retaining structure can, ifdesired, be a thermally conductive structure.

On the other hand, in an embodiment of a heat sensitive device designedto protect a heat sensitive device from its own self-generated internalheat, the endothermic compounds are poured into a container or supportedby a structure and the heat sensitive device is embedded therein. Ofcourse, if the heat sensitive device is embedded within the endothermiccompound, it is imperative to choose an endothermic compound whosetemperature of reaction is suitable for the particular application, andwhose decomposition and/or dehydration products will not affect the heatsensitive devices.

It is clear from the above that the position or location of theendothermic compounds is not fixed relative to the heat sensitivedevice, any outer structure supportive or its insulation. Rather suchposition or location in dependent on the application and the heatsensitive device's design specifications and heat tolerance. Similarly,the enclosure's shape is not limited. In fact, the shape and dimensionsthereof may or may not be limited by the application and the heatsensitive device's design specifications.

When the heat absorbing device comprises endothermic compounds within orlining it walls (either outer or inner), as is in the case of a heatabsorbing device designed to protect from external heat (see discussionabove), the heat sensitive device can be placed within the enclosureeither snugly, with no space between it and the walls of said enclosure;or loosely so that there is a defined space or a gap between it and theenclosure's walls.

If the heat sensitive device is placed so that it fits snugly within theenclosure, then the enclosure will be sealed to protect the heatsensitive device from the external high heat conditions, and the entirepackage can be further wrapped in insulation to further protect the heatsensitive device from the outside high temperatures.

On the other hand, if the heat sensitive device is placed so that itfits to form a gap between it and the heat absorbing enclosure, a layerof insulation can be placed in the gap between the heat sensitive deviceand the enclosure's walls. This adds another layer of protection againstthe outside heat. The enclosure is then sealed and if desired can befurther wrapped in another layer of insulation to further protect theheat sensitive device from the outside high heat.

In a preferred embodiment, however, of the heat absorbing devicedesigned to protect from external heat, said device is placed adjacentto the heat sensitive device; thereafter insulation is wrapped orsurrounded about the device and heat absorber and the entire package maybe placed in a housing.

In one application using the present invention, a flight data recorderis provided with a heat absorbing shield. The shield is in essence asingle, flat, rectangular block very similar to a small brick. It issized in length, height and width so that it could lie right up againstand contact the surface of the flight data recorder circuit board, whichrequires protection. The shield consists of wafers of boric acid heldtogether and retained with metal or plastic. The boric acid wafers areformed by compression into rectangular cakes, which fit neatly into theshield's metal or plastic retainer.

The boric acid shield is then laid up against the circuit board of thememory control system of the flight data recorder. The accompanyinggraphs 7 and 8 show the natural rise in temperature of a conventionalberyllium or wax heat sink when used with the flight data recorder, ascompared to the same flight recorder's thermal performance with a boricacid heat absorbing shield formed in accordance with the presentinvention described above.

In other applications of the invention, the flight recorder is placedwithin boric acid box-like structures; each differing only in thelocation of the boric acid, as described above. The structures are thensealed to protect the flight data recorder from the external high heatconditions and subjected to thermal loads in excess of fifty thousandwatts per one hour (1 watt=3600 joules; 1 cal=4,1850 joules), which isthe present government standard for testing flight recorders.

Again it was found that the flight recorder's thermal performance afterit was sealed within any of the boric acid structures taught above, wassubstantially better than the thermal performance of the same flightrecorder applying a conventional beryllium or wax heat sink thermallyprotective structure.

Graph 9 shows the use of a hydrated salt, i.e. MgSO₄.7H₂O in accordancewith the teachings set forth above, and how such use resulted in astrong cooling effect as applied to the flight recorder of Graph 7.

V. The ultimate shape, size and physical characteristics of the heatabsorbing device, as well as the type and amount of endothermic materialused, are dictated by many factors. These factors include the type ofheat sensitive device being protected; the time period for which theheat sensitive device will be exposed to high heat; the temperatures towhich the heat sensitive device will be ultimately exposed; and thethermal sensitivity of the heat sensitive device.

Thus, for example, if a flight recorder contains electronics made ofmaterials that are particularly sensitive to high heat, one might chooseto enclose the electronics completely within an endothermic andinsulated enclosure, as described above. On the other hand, if theelectronics are less sensitive to high heat, one might opt for the useof a single thin endothermic compound “shield”, as a thermal controlsystem.

Similarly, if the flight recorder will be exposed to very hightemperatures, as for example 600° C. through 1100° C. for more than justa few minutes, one would not only choose to enclose the flight recorderwithin an endothermic compound “box”, but one would use an endothermfrom those described above that decompose within that temperature rangei.e. Lithium Hydroxide, Sodium Hydroxide or Aluminum Hydroxide; or usemore insulation within the “box” and pick any of the endothermiccompounds disclosed above; or use multiple layers or mixtures ofdifferent endotherms, set to react at different temperatures. Moreimportantly, however, one would have to calculate, on the basis of theformulas set forth above, the amount of the endotherm(s) that wouldactually have to be contained within the “box” so that it couldefficiently and completely absorb the damaging thermal load, to whichthe flight recorder will be subjected.

On the other hand, if the flight recorder is going to be exposed totemperatures between 120° C. and 350° C., one can choose to enclose itwithin a boric acid “box.” The amount of boric acid within the walls ofthe “box” or the amount of boric acid surrounding the flight recordereither through its being poured onto the flight recorder, or through itsbeing lined onto the inner surface of the “box” can be calculated on thebasis of ΔH_(r)=(53,600 Kcal/2 mol) (2(62) g/2 mol≧432 cal/g.Specifically, one would have to calculate the amount of heat that theflight recorder would be exposed to over time. The method of saidcalculation is well known in the art. Thus, if the amount of damagingheat to which the flight recorder will be exposed over ten minutes willbe 432000 cal, then the amount of boric acid surrounding the flightrecorder in the box should be equal to or more than one thousand grams.

VI. Aluminum Hydroxide (Al(OH)₃) devices work best as high temperatureendothermic temperature control devices. When aluminum hydroxidedecomposes, it leaves behind a strong thermal insulation layer ofaluminum oxide (see above), which further abates a temperature risethrough its decomposition products which are deposited within the heatabsorbing device.

Other applications of the present invention presented, by way of exampleand not as a limitation include: temperature control coatings, wraps andliners, as well as thermal protection for metal and plastic structures;cooling for electronics, oven sensors, missile skins, exhaust pipes,thermal protection in race cars, fire walls, emergency cooling fornuclear reactors, guns, munitions boxes, batteries and relatedequipment; and in structures designed to shield life from thermal harm.

Unlike salt hydrates discussed above, hydroxides or carbonates may bestored almost indefinitely provided they are not exposed to temperaturesat or above the the temperature of reaction. When exposed to reducedpressure and some heat, hydrates tend to lose water, making them lesslikely to be fully effective as cooling agents in some aircraftapplications, unless properly hermetically sealed, with allowance topermit venting or water vapor at the temperature of reaction.

All of the endothermic compounds listed and discussed above arecommercially available and inexpensive. They may be easily incorporatedin and integrated in CFEMs, metal mesh matrices, silicon of carbon fiberor microencapsulated in porous silicate, porous carbon bodies, orsuspended in plastics such as fluoroelastomers, teflon, metals or othermaterials. The agents may be shaped in the form of enclosures, chips, orcakes which can be incorporated in shaped bodies, and thus, can beformed in shape and dimension as required. In some applications theagents may be formed into gels and pastes.

The special compounds of the present invention provide unforeseen,critical benefits in that they readily absorb massive quantities ofheat, in a unidirectional reaction. And that once they absorb it, theydo not release it, they do not reverse, and therefore cannot act as heatgenerating compounds. Thus, protection for heat sensitive devices issignificant and substantial within a closed environment.

Furthermore, all of these compounds produce environmentally harmlessvapor products during decomposition and even at elevated temperatures.In addition, since these compounds are per se generally non-toxic (ascompared to Beryllium, a material used in prior art heat sinks and whichis extremely toxic) they are easier and less expensive to use in themanufacturing process of the heat absorbing devices.

Various modifications and changes have been disclosed herein, and otherswill be apparent to those skilled in this art. Therefore, it is to beunderstood that the present disclosure is by way of illustration and notlimitation of the present invention.

What is claimed is:
 1. A method for preventing the increase oftemperature in heat sensitive devices through the absorption of heatduring heat generating conditions comprising the steps of: (a) providingan amount of hydrated salt sufficient to effect the required heatabsorption, said hydrated salt being selected from the group consistingof hydrated salts of Lithium Chloride, Magnesium Chloride, MagnesiumSulfate, Sodium Sulfate, Aluminum Oxide, Aluminum Sulfate, AluminumFluoride, Aluminum Nitrate, Lithium Nitrate, Sodium Borate, BerylliumSulfate, Sodium Phosphate, Calcium Chloride, Zinc Sulfate, AluminumChloride, Zinc Chloride and the mixtures thereof; and (b) supportingsaid hydrated salt in a position between the heat sensitive device and aheat generator; so as to absorb the heat and prevent any increase in thetemperature of the heat sensitive device.
 2. A method for preventing theincrease of temperature in a heat sensitive device through theabsorption of the heat sensitive device's self-generated heat, duringheat generating conditions, comprising the steps of: (a) providing anamount of hydrated salt sufficient to effect the required heatabsorption, said hydrated salt being selected from the group consistingof hydrated salts of Lithium Chloride, Magnesium Chloride, MagnesiumSulfate, Sodium Sulfate, Aluminum Oxide, Aluminum Sulfate, AluminumFluoride, Aluminum Nitrate, Lithium Nitrate, Sodium Borate, BerylliumSulfate, Sodium Phosphate, Calcium Chloride, Zinc Sulfate, AluminumChloride, Zinc Chloride and the mixtures thereof; and (b) contactingsaid hydrated salt to the heat sensitive device; so as to absorb theheat sensitive device's self generating heat and prevent any increase inits temperature.
 3. A method for preventing the increase of temperaturein a heat sensitive device through the absorption of the heat sensitivedevice's self-generated heat, during heat generating conditions,comprising the steps of: (a) providing an amount of hydrated saltsufficient to effect the required heat absorption, said hydrated saltbeing selected from the group consisting of hydrated salts of LithiumChloride, Magnesium Chloride, Magnesium Sulfate, Sodium Sulfate,Aluminum Oxide, Aluminum Sulfate, Aluminum Fluoride, Aluminum Nitrate,Lithium Nitrate, Sodium Borate, Beryllium Sulfate, Sodium Phosphate,Calcium Chloride, Zinc Sulfate, Aluminum Chloride, Zinc Chloride and themixtures thereof; and (b) indirectly contacting said carbonate salt tothe heat sensitive device; so as to absorb the heat sensitive device'sself generating heat and prevent any increase in its temperature.
 4. Amethod of using a hydrated salt in an amount sufficient to absorb apredetermined amount of heat comprising the step of directly orindirectly contacting the hydrated salt to a heat sensitive device,wherein said hydrated salt is selected from the group consisting ofhydrated salts of Lithium Chloride, Magnesium Chloride, MagnesiumSulfate, Sodium Sulfate, Aluminum Oxide, Aluminum Sulfate, AluminumFluoride, Aluminum Nitrate, Lithium Nitrate, Sodium Borate, BerylliumSulfate, Sodium Phosphate, Calcium Chloride, Zinc Sulfate, AluminumChloride, Zinc Chloride and the mixtures thereof.